Is there anything wrong with using lambda for winforms event?

Question

This is a very simple question. I'm asking because I've never seen it before which makes me wonder if there's something wrong.

comboBox1.MouseEnter += (a, b) => comboBox1.Focus();
campaignDataGridView.MouseEnter += (a, b) => campaignDataGridView.Focus();

Answer 1

This is perfectly acceptable, however, since these are anonymous delegates, there is no way to unsubscribe the event handler.

That is:

// Subscribe lambda as event handler
comboBox1.MouseEnter += (a, b) => comboBox1.Focus(); 

// Try to unsubscribe a _different_ lambda with identical syntax. 
// The first lambda is still subscribed
comboBox1.MouseEnter -= (a, b) => comboBox1.Focus(); 

Whether that is a problem or not depends on your application and use.

Answer 2

It is fine; the only subtle point is if you need to unsubscribe it; then you need to store the delegate locally too:

EventHandler handler = (s,a) => ...
obj.SomeEvent += handler;
...
obj.SomeEvent -= handler;

Note that if I'm not using either parameter (sender/args) I prefer the anon method syntax:

obj.SomeEvent += delegate {...};

As this doesn't introduce any extra (unnecessary) variables into scope.